Rapid scanning antenna directive system



April 26, 1960 C. HOPKINS RAPID SCANNING ANTENNA DIRECTIVE SYSTEM Filed Feb. 28, 1949 2 Sheets-Sheet 1 19 I I? Q ERROR SIGNAL m kfi l8 lo FOGUSING l DEVICE a RANGE mmcAToRw ELIE-m4 l I I0 INVENTOR.

CLEVELAND HOPKINS BY 2 2% I ATTORNEY,

P 25, 1960 c. HOPKINS 2,934,763

RAPID SCANNING ANTENNA DIRECTIVE SYSTEM BEARING ERROR SIGNAL I L ELEVATION ERROR SIGNAL RANGE BOX IN DICATOR IIE 7 TRANSMITTER TFEGB IIIII I 1% -l L Illl I I CLEvELAND I- l l l fis "I By W A A TTORNEY RAPID SCANNING ANTENNA DIRECTIVE SYSTEM This invention relates generally to antennas and more particularly to a rapid scanning device for highly directional antennas.

Through the medium of micro-wave radiant energy, narrow beam antennas have been developed having azimuth and/or elevation resolution formerly obtainable only byantenna lobe switching. Such high resolution is provided by energizing a suitable number of electromagnetic horns which are interconnected by four terminal networks or other similar devices wherein the difference in signal level at selected horns is continuously measured without the need for physical lobe switching. Such an antenna is disclosed in the copending application of William L. Briscoe, Serial No. 4,052, filed January 23, 1948, for New Type Directive Antenna System, now abandoned.

It is well recognized that narrow beam antennas have such a reduced field that their use in radar and directon finding problems makes the initial locating of a target extremely diflicult. This condition has been improved by swinging the antenna beam so that it rapidly scans a larger area. However, the mechanical means used to provide rapid scanning have been unduly complicated and are not practicable for antennas using multiple electromagnetic horns due to the relative high moment of inertia of the horn system.

Accordingly, it is an object of this invention to provide an improved rapid scanning system of multiple element, narrow beam antennas.

It is another object of this invention to provide rapid scanning of multiple electromagnetic horn antennas with Y a minimum of apparatus.

It is another object of this invention to provide a rapid scanning system suitable for use with electromagnetic horns interconnected to provide sum and difference outputs.

Other objects and advantages of this invention will be apparent from the following description and the accompanying drawings wherein similar characters of reference indicate similar parts throughout the several views.

In the drawings,

Fig. 1 is an isometric side elevation view of a representative embodiment of this invention;

Fig. 2 is an enlarged isometric elevation view of a portion of Fig. 1,

Figs. 3, 4, 5 and 6 portray antenna field patterns obtained by this invention;

Fig. 7 is a diagrammatic view of a variant embodiment of this invention and Fig. 7A is an elevation of the radiating elements of Fig. 7;

Fig. 8 is a top plan view of the radiating elements of Fig. 1..

Briefly, this invention provides a system for effectively extending the beam width of multi-element narrow beam antennas without reducing their high resolution characteristic. I have found that moving one radiating element forward or backward with respect to the other elements of a multi-element array angularly shifts the I atent 2,934,763 Patented Apr. 26, 1960 antenna beam. Displacing a radiating element a quarter wave length produces a maximum amount of shift which may be measured as one-half the beam width of the single horn. Displacements greater than one-quarter wave length cause the beam shift to repeat once for each addi tional quarter wave length. Consequently a very rapid scanning efiect may be developed in a pair of electromagnetic horns simply by imparting a reciprocating mo tion to the horns. The required motion for maximum beam shift is so slight that a short length of ordinary wave guide will absorb the flexing, hence sliding contacts and resultant changing of the feed line length will be avoided. As is further described below, a pair of horns may be thus used to provide scanning of either azimuth or elevation and four horns may be used to provide scanning of both azimuth and elevation.

Referring to Fig. 1 in detail, an elevational view of an exemplary rapid scanning arrangement according to this invention is shown in association with a block representation of a radar automatic follow-up system. A pair of electromagnetic horns 10 and 11 are shown as the radiating elements. These horns are parallel fed from a four terminal network 12 through two symmetrical lengths of wave guide 13 and 14. The wave guide lengths 13 and 14 are suitably disposed and arranged so as to have exactly equal lengths or lengths differing by an even multiple of half wave lengths in order to insure in-phase feeding of horns 10 and 11.

The vertical portions of wave guides 13 and 14 are made long enough to offer some flexibility across their smallest dimension, thereby permitting small axial displacements of horns 10- and 11. A vertical height of 14 inches has been found entirely adequate with the standard 1 x /2 wave guide for quarter wave displacement at a nominal wave length of 3 cm. The displacing force is applied to horns 10 and 11 alternately since the desired effect is the alternate displacement of one horn with respect to the other. This effect may be achieved, for example, by placing cams against one or both of said horns. A preferred arrangement is shown in Fig. 1 wherein cams 16 and 17 ride against the upper ends of wave guides 13 and 14. These cams are driven by a motor 18 and are disposed to alternately drive their respective horn ahead of the other horn as will be apparent from the configuration of cams 16 and 17 as shown in Fig. 1.

It is desirable to place an electromagnetic focusing device 19 in front of the horns to concentrate the beam and thus extend the range of the equipment. The focusing device 19 is typically a lens or a parabolic reflector, however, for the embodiment of Fig. 1 a lens is preferred since the vertical wave guide portions and the cams would tend to obstruct radiation from a reflecting device. It will be readily understood, however, that the upper knees of wave guides 13 and 14 could be replaced by U-shaped members having their lower arms extending through an aperture in a parabolic reflector. The reciprocating motion could then be imparted to the horns by driving the lower arms of each U from behind the reflector.

In Fig. 1 the antenna is shown in operation with an automatic tracking system, which as shown will operate to keep the antenna trained upon a moving target. Pulse energy is fed from transmitter 20 to the sum terminal 21 of the four terminal network 12. The transmitter energy is applied to wave guides 13 and 14 through the T connection in network 12 and appears with equal mag nitude at the T outlets 22 and 23. The energy is thus fed in phase to horns 10 and 11 since wave guides -13 and 14 are of equal length. Reflected energy picked up by horns 10 and 11 is returned by the equal length wave guides to the network 12. As further explained in connection with Fig. 2, reflected energy received inphase at horns and 11 will appear at the diiference terminal 24 of the network only if it is received by horns 10 and 11 with unequal intensity. Any difierence signal is then an error signal indicating that the antennas are not directly on target and it may be fed to a servo position correcting device 25. There the difference signal is translated into mechanical energy and may be applied through mechanical linkage 26 to the antenna support 27 to train the antenna upon the target. By inserting a T-R box 28 between the transmitter and the sum terminal 21, indications of range may be obtained from the sum terminal by connection to any suitable range indicator 29.

The four terminal network 12 is shown in Fig. 2 as seen looking into the sum terminal 21. Connection to horns 10 and 11 is diagrammatically represented. The horns 11 and 10 are respectively receiving signals A and A which are of equal magnitude and the same phase. The phase of signals A and A at different points in the network is shown by arrows to demonstrate the summation and cancellation properties of network 12. More particularly, it will be seen that signals A and A be come of opposite phase in diiference terminal 24, and since they are of equal magnitude, will cancel. But in sum terminal 21 the signals retain their in-phase relation and will add.

Fig. 3 is a plan view of the normal overlapping antenna patterns of horns 1G and 11, while Fig. 4 shows how these antenna patterns are effectively modified by the use of the T network 12. The single envelope 30 is the summation pattern looking into the sum terminal 21 and the double envelope 31 is the error signal producing pattern seen looking into the difference terminal 24. The sharp resolution of the error obtainable by the T network is apparent from the small area of the pattern 31 in which the field strength of horns 10 and 11 are exactly equal and no output signal appears at diiference terminal 24. This appears in Fig. 4 as the null in the center of pattern 31.

Fig. 5 is a plan view of the antenna pattern with the horns alternately displaced one-quarter wavelength in the manner taught by this invention. Pattern 30 of Fig. 4 is swung one-half beam width to the left as shown by pattern 32 of Fig. 5 by the forward movement of horn 10 one-quarter wavelength. Similarly, pattern 30 is swung one-half beam width to the right as shown by pattern 33 of Fig. 5 when horn 11 is moved one-quarter wavelength forward of horn 10. This latter position of the horns is that shown in Fig. 1.

Fig. 6 is a head on view of the antenna patterns of Figs. 4 and 5 wherein patterns 32 and 33 are shown by dotted lines to indicate the extent to which the area of pattern 30 can be extended by the reciprocal movement of horns 10 and 11.

In many applications of electromagnetic horn radiators it is desirable to determine and follow accurately the targets elevation as well as hearing. For this purpose four horns may be used, and are typically arranged in layers of two as portrayed by horns L, M, F and T in Fig. 7A. Fig. 7 illustrates schematically a typical interconnection of said horns to provide elevation and hearing error signals. The horizontal pairs of horns L, M and F, T are each interconnected by four terminal networks 40 and 41 in the same manner as horns 10 and 11 of Fig. 1. Accordingly the bearing error signal may be taken from the difierence terminal of either networks 40 or 41 or both in parallel. S is used to designate the sum terminal and D the difference terminal throughout the drawings. By connecting the sum terminals of networks 40 and 41 to opposite terminals of a third four terminal network 42, an elevation error signal can be produced at the difiierence terminal of said third network 42. It will be apparent that elevation signals could be obtained as well from either vertical pair of horns L, F, or M, T alone.

It will be seen, therefore, that this invention may be applied to the more versatile antenna arrangement of Fig. 7 to provide an even greater increase in the search field of the antenna. Cams 43, 44, 45 and 46 are diagrammatically represented in Fig. 7 to reciprocally move horns L, M, F and T respectively. The cams are connected to a common shaft 47 driven by motor 18. The cams are suitably oriented on shaft 47 to successively drive horns L and F forward (in the position shown), then horns F and T forward, then horns T and M forward, and then horns L and M forward. This completes one cycle and the movement will then repeat. When horns F and T are forward the beam will be moved up and when horns L and M are forward the beam will be moved down. And when horns L and F are forward the beam will be moved to one side and to the other side when horns M and T are forward. The up and down movement of the antenna beam 30 is shown by dotted lines 48 and 49 in Fig. 6. It will be understood that the cams might readily be designed to also provide alternate movement of a single horn with respect to the other horns, thus filling in the corners of the pattern in Fig. 6 to provide a composite pattern in the shape of a circle including and tangent to the four circles 32, 33, 48 and 49.

Fig. 8 is a top plan view of the horns 10 and 11 of Fig. l. In this view the horns are drawn to scale and represent 1" horns terminating the standard 1" by /2." wave guide. The horns as shown here and in Fig. 1 represent a preferred form, however, horns having other configurations may be readily substituted. It is noted that, for example, horns with wider mouths have a Wider beam width, however, the angular beam shift obtainable by this invention is still one-half beam width of the single horn. As in Fig. 1, horn 11 is shown advanced onequarter wavelength as determined by the frequency having a nominal wavelength of 3 cm. It will be seen from Fig. 8 that only a very small movement of the horns is required, just over a quarter inch at this frequency to obtain quarter wavelength displacement of the horns. It therefore is apparent that very high scanning rates are possible and in fact a scanning rate of 60 per second is easily obtained by this invention, higher rates are possible with careful mechanical design.

Although only certain representative embodiments of this invention have been shown and described, it is ap parent that the antenna scanning system herein disclosed may be applied to radio direction finding, to sector scan radars by synchronizing an azimuth sweep with the movement of the horns, and it may be modified to operate with such other known radiating devices as dipoles or slots instead of electromagnetic horns. Many modifications or variations such as described above may, of course, be made without departing from the spirit and scope of the invention as defined in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

l. A rapid scanning directive antenna comprising at least one pair of directive antenna elements disposed in broadside array, means interconnecting the antenna elements to feed them in phase from a common point, reciprocal motion generating means engaging said antenna and operative to reciprocally displace at least one of said antenna elements from the other elements along the normal axis of directivity.

2. A rapid scanning directive antenna comprising a plurality of directive antenna elements disposed in broadside array, reciprocal motion generating means engaging said antenna and operative to consecutively displace certain of said antenna elements from the other elements, said displacement being made along the normal axis of directivity.

3. A rapid scanning directive antenna comprising a pair t the other, said displacement being made along the noranal axis of directivity.

4. A rapid scanning directive antenna comprising uppet and lower pairs of directive antenna elements stacked in broadside array, three four terminal networks, two

ing means engaging said elements and operative to consecutively displace selected groups of two of said antenna elements from the unselected two elements, said displacement being made along the normal axis of directivity,

References Cited in the file of this patent UNITED STATES PATENTS 2,156,653 Ilberg May 2, 1939 2,166,991 Guanella July 25, 1939 2,412,631 Rice Dec. 17, 1946 2,462,102 Istvan Feb. 22, 1949 2,480,829 Barrow et a1. Sept. 6, 1949 FOREIGN PATENTS 694,523 Germany Aug. 2, 1940 

